Recently, due to downsizing of semiconductor devices, a lot of functions are implemented on a semiconductor integrated circuit. In order to realize general-purpose properties, it is common that circuits which are used for a certain application but not used for another application are implemented on a semiconductor integrated circuit and selected by users whether a specific function is used or not.
If power is not supplied to a circuit which is not used for a certain application to reduce the power consumption, output signals of the circuit become uncertain values or high impedance state. If a signal of the uncertain value or the high impedance is connected to another circuit being used, leakage current may occur and result in large power consumption, or the circuit may malfunction. To prevent the problem, there is a solution to provide signal propagation control circuit on the integrated circuit between the circuits and prevent the propagation of the uncertain value or the high impedance to the circuit being used. In this case, a dedicated terminal is necessary to define the usage of the function because the information whether a function is used or not, is necessary to control the signal propagation control circuit during the ramp-up period of the integrated circuit. However it increases the number of terminals of the integrated circuit.
If the additional terminal is not allowed due to area constraints, the signal propagation control circuit cannot be used. Therefore, even a circuit which is not used for a certain application must be provided with power and it may result in large power consumption.